btrfs: Open code btrfs_write_and_wait_marked_extents

btrfs_write_and_wait_transaction is essentially a wrapper of
btrfs_write_and_wait_marked_extents with the addition of calling
clear_btree_io_tree. Having the code split doesn't really bring any
benefit. Open code the later into the former and add proper
documentation header.
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ reformat comment ]
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/transaction.c

@@ -1083,40 +1083,33 @@ int btrfs_wait_tree_log_extents(struct btrfs_root *log_root, int mark)
 }
 
 /*
- * when btree blocks are allocated, they have some corresponding bits set for
- * them in one of two extent_io trees.  This is used to make sure all of
- * those extents are on disk for transaction or log commit
+ * When btree blocks are allocated the corresponding extents are marked dirty.
+ * This function ensures such extents are persisted on disk for transaction or
+ * log commit.
+ *
+ * @trans: transaction whose dirty pages we'd like to write
  */
-static int btrfs_write_and_wait_marked_extents(struct btrfs_fs_info *fs_info,
-				struct extent_io_tree *dirty_pages, int mark)
+static int btrfs_write_and_wait_transaction(struct btrfs_trans_handle *trans,
+					    struct btrfs_fs_info *fs_info)
 {
 	int ret;
 	int ret2;
+	struct extent_io_tree *dirty_pages = &trans->transaction->dirty_pages;
 	struct blk_plug plug;
 
 	blk_start_plug(&plug);
-	ret = btrfs_write_marked_extents(fs_info, dirty_pages, mark);
+	ret = btrfs_write_marked_extents(fs_info, dirty_pages, EXTENT_DIRTY);
 	blk_finish_plug(&plug);
 	ret2 = btrfs_wait_extents(fs_info, dirty_pages);
 
+	clear_btree_io_tree(&trans->transaction->dirty_pages);
+
 	if (ret)
 		return ret;
-	if (ret2)
+	else if (ret2)
 		return ret2;
-	return 0;
-}
-
-static int btrfs_write_and_wait_transaction(struct btrfs_trans_handle *trans,
-					    struct btrfs_fs_info *fs_info)
-{
-	int ret;
-
-	ret = btrfs_write_and_wait_marked_extents(fs_info,
-					   &trans->transaction->dirty_pages,
-					   EXTENT_DIRTY);
-	clear_btree_io_tree(&trans->transaction->dirty_pages);
-
-	return ret;
+	else
+		return 0;
 }
 
 /*